共聚亚胺塑料

本文介绍难熔聚酰亚胺 ,通过共聚方法改进加工性能 ,并在较低温度和压力下成型 ,通过热处理 ,提高PI塑料的热变形温度 ,达到高温使用的目的。     

氯化聚丙烯市场与技术分析研究

介绍了氯化聚丙烯的性能、用途、制备方法和国内外生产与市场状况。探讨了我国氯化聚丙烯发展方向并提出了建议。     

Numerical simulation of the thermal history multiple laser deposited layers

Multilayer direct laser metal deposition is a fabrication process in which the parts are fabricated by creating a molten pool into which metal powder particles are injected, and a layer is laid down by moving the pool. Height is added by creating additional layers on top of the first layer. During fabrication, a complex thermal history is experienced in different regions of the build. The thermal history includes the reheating process for previously deposited layers caused by subsequently deposited layers. The objective of this study is to provide insight into the thermal history during the direct laser deposition process. Using the commercial ABAQUS/CAE software, a thermomechanical 3D finite element model was developed. This work presents a 3D heat transfer model that considers the continuous addition of powder particles in the front of a moving laser beam using ABAQUS/CAE software. The model assumes the deposit geometry appropriate to each experimental condition and calculates temperature distribution, cooling rates, and remelted layer depth which can affect the final microstructure. Model simulations were qualitatively compared with experiments results acquired in situ using a K-type thermocouple.     

Integrated load‐based power saving for BS and MSS in the IEEE 802.16e network

In our previous work, the limitation of standard type I and II power saving in IEEE 802.16e was discussed, and the idea of load‐based power saving (LBPS) was proposed for better power‐saving efficiency. LBPS measures traffic load and adaptively generates proper sleep schedule for the current load. Three LBPS schemes have been proposed for mobile subscriber station (MSS) power saving. In this paper, base station (BS) power saving is taken into consideration, and our previously proposed LBPS schemes, are extended and revised to integrate both BS and MSS in sleep scheduling. Two strategies of integrated power saving, MSS first and BS first, each with associated LBPS schemes are proposed in the paper. A three‐staged concept combining the proposed strategies is also presented to make the best of integrated power saving. A simulation study shows that the proposed schemes can effectively achieve high power‐saving efficiency for both BS and MSS. Copyright © 2013 John Wiley & Sons, Ltd.     

A mixture design approach to optimizing the cathodic compositions of proton exchange membrane fuel cell

Cathodic catalyst layers for proton exchange membrane fuel cells (PEMFCs) are prepared according to a spraying technique, and the optimal composition of the catalyst layer is investigated by applying a mixture design approach, where the power density of the PEMFC is used as the response of the model. Based on the conventional experimental design, the optimal Nafion content of the electrocatalytic layers of a PEMFC is 35%, and a maximum power density (P_max) of 239.5 mW cm⁻² is attained. Polytetrafluoroethylene (PTFE) is added to the cathodic catalyst layer to manage water, and the relationship between the P_max of the PEMFC (y) and the cathodic pseudo-compositions (Y₁ (Pt/C), Y₂ (Nafion) and Y₃ (PTFE)) is obtained:

y=204.40Y₁+198.60Y₂+188.44Y₃+167.46Y₁Y₂ (R²=0.9908)     

数字测速方法及其电路

本文系统地介绍了四种测速方法。其中 M 法、T 法、M/T 法是人们已经熟悉的。文中提出了如何使线路最简的实例。对 KT 法,较系统地介绍了其原理和电路,它是一种在很宽范围都有很高的测速精度和最小计算量的测速方法。对四种测速方法都进行了评价。